<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="js/jquery.min.js"></script>
    <style>
        div{
            position:fixed;
            width: 100px;
            height: 100px;
            background-color:pink;
        }
    </style>
</head>
<body>
    <div></div>
    <script>
        function fn(a,b,callback){
            console.log(a+b);
            (callback instanceof Function) && callback();
        }
        // fn(1,2,4);
        fn(1,2,function(){
            console.log('我是最后调用的');
        });

        $('div').animate({left:500},function(){
            $('div').css("backgroundColor","purple");
        });
    </script>
</body>
</html>